*{
    margin: 0;
    padding: 0;
}

body,html{
    width: 100%;
    height: 100%;
}
.nav-box{
    width: 200px;
    background: rgb(50, 65, 87);
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    overflow-y: auto;
    padding-top: 40px;
}
.nav-two a:link{
    color: #fff;

}
.nav-two a:link{
    color: #fff;
}
nav-block a:link{
    color: #fff;
}
.nav-box ul{
    list-style: none;
    line-height: 50px;
    font-size: 14px;
    color: #ddd;
}
.nav-box ul .nav-block{
    padding-left: 10px;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: flex-start;
    flex-wrap: wrap;
    position: relative;
    font-size:20px;
    padding-top: 10px;
    margin-top: 20px;
}
.nav-box ul .nav-block:hover{
    color: #fff;
    background: rgb(40, 52, 70);
}
.nav-box ul li i{
    display: inline-block;
    width: 40px;
    height: 40px;
}
.nav-box ul li i.arrow{
    position: absolute;
    top: 5px;
    right: 5px;
}


.nav-box .nav-block.on i.arrow{
    transform: rotate(0deg);
}
.nav-box .nav-two{
    display: block;
    width: 100%;
    font-size: 13px;
    line-height: 45px;
    display: none;
}
.nav-block.on+ul.nav-two{
    display: block;
}
.nav-box .nav-two li{

    padding-left: 38px;
    cursor: pointer;
}
.nav-box .nav-two li:hover{
    background: rgb(40, 52, 70);
}
.header{
    border: solid 1px black;
    width: 1800px;
    height: 60px;
    background: green;
    
}
.header h1{
    text-align: center ;
    font-size: 50px;
    font-family: 隶书;
    letter-spacing: 20px;
    position: relative;
}
.return {
    width:600 px;
    height: 30px;
    position: absolute;
    top: 20px;
    left: 1550px;
    font-size: 30px;
}
.return a{
    text-decoration: none;
}    
:root {
    --text-primary: #1a1a1a;
    --background: #f8f9fa;
    --primary: #0066cc;
    --contrast: #ffd700;
}
/* 高对比度模式 */
.a11y-high-contrast {
    --text-primary: #FFFFFF;
    --background: #000000;
    --primary: #FFD700;
    --contrast: #00BFFF;
}
/* 阅读障碍模式 */
.a11y-dyslexia {
    font-family: 'OpenDyslexic', sans-serif;
    letter-spacing: 0.1em;
    line-height: 1.8;
}
body {
    background: var(--background);
    color: var(--text-primary);
    font-family: system-ui, sans-serif;
}
/* 无障碍工具栏 */
.a11y-toolbar {
    position: fixed;
    top: 0;
    right: 0;
    background: rgba(255,255,255,0.9);
    padding: 1rem;
    z-index: 1000;
    display: flex;
    gap: 1rem;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
}
.a11y-button {
    padding: 0.5rem 1rem;
    border: 2px solid var(--primary);
    background: none;
    cursor: pointer;
    transition: all 0.3s ease;
}
/* 课程卡片 */

.course-card {
    width: 550px;
    background: white;
    border-radius: 8px;
    padding: 2rem;
   margin-left: 200px;
    margin-top: 100px;
    max-width: 800px;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
    position: relative;
    float: left;
}
.course-card:focus {
    outline: 3px solid var(--contrast);
}
/* 语音控制提示 */
.voice-command-hint {
    position: fixed;
    bottom: 2rem;
    left: 50%;
    transform: translateX(-50%);
    background: var(--primary);
    color: white;
    padding: 1rem 2rem;
    border-radius: 50px;
    animation: pulse 2s infinite;
}
@keyframes pulse {
    0% { opacity: 0.8; }
    50% { opacity: 1; }
    100% { opacity: 0.8; }
}
/* 手语视频模块 */
.sign-language {
    position: relative;
    margin: 2rem 0;
}
.sign-language video {
    width: 100%;
    border: 3px solid var(--primary);
}